In the last two decades there have been drastic changes in the pattern of petroleum fuel consumption, while the quality of the crude oil produced has notably diminished. In the industrialized countries, the environmental restrictions on pollutant emissions, such as sulfur and nitrogen oxides, the growth of the nuclear industry and the growing utilization of coal and natural gas in the generation of energy, have reduced the demand for residual fuels and increased the need for light and intermediate fuels like gasoline and jet and diesel fuel.
On the other hand, the percentage of heavy crude oils in proved world reserves has increased. As a result of this increase, the quality of the average mixture of crudes is constantly decreasing.
Consequently, the increasing demand for higher quality light fuels can only be covered, starting from residues and heavy crudes, by utilizing more stringent technologies.
Various technologies for treating barrel bottoms have been developed, particularly in the last two decades. However, such approach has centered on the conversion of vacuum residues of the crudes now processed, all of them light and intermediate types, although in some refineries heavy crudes are processed in mixtures with lighter crudes.
In fact, efforts made toward processing heavy crude have been few, because the majority of the world's refineries at present are set up to process light crudes.
The conventional process of extraction by solvent, classified among the techniques for the improvement of heavy fractions due to the elimination of carbon, constitutes an economical short term alternative for a conventional refinery ordinarily refining light crudes and in which heavy crudes are desired to be processed.
Traditionally, in the process of extraction with solvents, a vacuum residue is processed as in U.S. Pat. No. 2,847,353. Other processes such as U.S. Pat. No. 3,951,181, mix the vacuum residue with an atmospheric gas oil and feed it to the extraction section, thereafter processing the residue obtained by catalytic cracking. Other patents like U.S. Pat. No. 4,389,302 and U.S. Pat. No. 3,379,639 feed the residue obtained from the extraction process to a vis-breaking process.
Other processes such as those previously mentioned for U.S. Pat. No. 3,379,639, as well as for U.S. Pat. No. 3,637,483, feed atmospheric residues of light crudes into the process, obtaining a good quality extract which can be directly subjected to hydrotreatment as in U.S. Pat. No. 3,379,369 or else its vacuum residue as in U.S. Pat. No. 3,637,483. Also, in the latter (U.S. Pat. No. 3,637,483), this process is used as an important step in obtaining lubricants. Vacuum residue is used in feeding the extraction stage. The previously mentioned processes principally process light and intermediate crudes. The present invention is directed towards processing heavy crudes, and the residue of the extraction stage is not only used in asphalts, but is used to produce metallurgical coke in mixture with coals.